The original article says construction is continuing. Not ‘has continued since we last took satellite images.’

But that's exactly what they mean.

If you look at the website, they run a series of articles under the topic Satellite Imagery, wherein they get some new satellite photos of a particular location in North Korea and compare those photos to the previous sets of satellite photos they have, noting any changes: new buildings, new walls, new smoke visible etc.

For example here is the recent series of articles about the Yongbyon Nuclear Research Facility, the location we are concerned with:

June 26, 2018 article using satellite photos taken on June 21.
May 30, 2018 article using satellite photos taken on May 6.
April 6, 2018 article using satellite photos taken on April 4.
March 30, 2018 article using satellite photos taken on March 20.
March 5, 2018 article using satellite photos taken on February 25.

So whenever they say "is continuing" they really mean "has continued since we last took satellite images", because the comparison of satellite imagery is the sole basis for their conclusions.

It's also important to note that the dates of the satellite images are spaced out. They only get a set every few weeks or so.

To make judgements about what has taken place since the summit (held on June 12th) we would need two sets of photos taken after June 12th on different dates (so we could unequivocally see any changes). But there is no evidence in the article for two sets taken after the summit.