Just to pick up on this heading:

His Flirting Is Consistent

There could be many reasons why flirting may be inconsistent that have nothing to do with the other quite reasonable points in this article.

1. He might be sensitive to context, i.e. if a location feels more intimate or private, then flirting is easier, if more open and public, less so. Of course, as the relationship progresses that concern (if it exists) should lessen. However, some people are just more choosy about the time and place for flirting.
2. He might not be sure if his attempts at flirting were accepted/appreciated last time so he’s toning it down so as not to blow things this time/overall. Most guys will have crossed the line between flirty and creepy at some time — hopefully they were told because it can be a difficult line to draw, especially as it’s down to how receptive she is as well as what’s said.
3. He’s just as prone to being tired or hangry as all people are, which will always impact on flirting. Alternatively, something else might be on his mind — how personal that thing is and how far into the relationship you are will define how likely he is to tell you what that thing is and whether he can be vulnerable (one of the other points in the article). It’s entirely possible that he sees spending some time with you as a way to get out of his head and away from whatever this other thing is and he may be just as upset that he’s finding it difficult to remain focussed on you and be in the moment.

In other words, and not to say that this was suggested in the article, but inconsistency in flirting (and indeed all of the points raised) shouldn’t be taken, in isolation, as lack of interest unless it persists over time… and even then he might just think that he’s not good at flirting, so doesn’t do it much.