Let's take both accounts into consideration and form a hypothesis out of each. OP's hypothesis is that the liquid was from the smoothie and was spilled, and the "prosecution" hypothesis would be that OP murdered the victim.
There are several points here to note.
- You don't see any drops leading away from the location. You would expect to find cast off spatter in the forms of drops away from the location.
- The amount of liquid is less than a litre. An average person has between 5 and 6 litres of blood in their system. They can lose a pint of blood (around ½litre) and not suffer any effects. A pint is a lot of liquid. Try take a pint of tomato juice and spill it on the floor and see how much surface area will be covered. You’ll be surprised by how much will be covered, and you still won’t even faint from that (unless you’re squeamish). Now add another pint to the floor surface, that’s now the limit before we would get negative effects. Generally, losing a litre of blood is not lethal and a person would recover easily from this with proper first-aid and medical care. It is therefore very unlikely that the victim would die from the attack.
- All stains are not higher than the bar on the wall. If the victim was murdered while lying face down on the table then we would have found more stains on the table than what already is there now; if the victim was murdered sitting upright then (depending on the weapon used) we would find either arterial spatter on lower wall and all over the table or cast off spatter on the wall above the bar. Therefore we must consider that the victim could have been murdered standing up while leaning on top of the chair. This would be consistent with the amount of cast off spatter and arterial spatter on the floor and chair.
- There is blood underneath the chair's legs which could mean that the chair is not in its original position and therefore has been moved. This is called transfer stain which can either be the absence of a stain or stains in the form of swipes/wipes.
- The angle of the picture does not reveal much of the seat although a few stains can be seen in the shade. If there is a significant amount of stains on the seat then that has to be accounted for as well: Are those stains cast off spatter or arterial spatter, or are they transfer stains? If the former then the victim could have either spilled the liquid while standing or leaning over the chair. If the latter then those stains could be swipes by the victim.
- All the cast off spatter are very large and have several satellite drops leading away from the chair. As mentioned above, the liquid must have been dispersed from the chair and in a rapid and swinging motion. This means that they could not have come from any weapon but directly from the source, most likely from the head and/or neck area while sitting or leaning over the chair. In particular, you would find a spray pattern on the wall and table since the victim would cough up blood if the neck were cut. It would however be unlikely that a victim once attacked would start to gush out blood in all these directions at once without hitting the wall above the bar and the table. The distribution of the stains fit better with that of a set amount of liquid from a set location perhaps in a container.
- The colour of the liquid is very important. It is red and therefore presumptive tests should have been made prior to examination, tests such as Kastle-Meyer to establish whether it is blood. However, a trained blood pattern analyst would probably not consider this to look like the characteristics of blood. The pattern on the back of the chair is dry. Dry blood usually has a brownish hue, unlike the movies.
Although it is difficult to say which hypothesis is the right one, I lean towards OP’s hypothesis due to the fact that the colour of, the amount of and distribution of the stains would not satisfy the criteria set by the prosecution hypothesis. A forensic scientist can never say exactly what happened, only the likelihood of the events, matches, contact, etc. It is therefore my conclusion that it is unlikely that the liquid is blood or that the victim was murdered or even attacked.