I don't think it's entirely ridiculous to suggest that Johnson's statements are "talking up war", both in terms of the chances of it breaking out, and also in its likely seriousness.
Some of what we've seen comes across as if a Russian invasion of Ukraine is now more or less a certainty, which strikes me as an exaggeration (which is not me saying that invasion is an impossibility).
And the stuff about the biggest war since 1945 and about how an invasion of the Ukraine would merely be the first step to the Russian annexation of half of Eastern Europe. Again, this strikes me as an exaggeration.
As to his possible reasons for doing it, I'm pretty sure it's not because he cares about anyone in Ukraine, or even because it's a serious attempt at a useful diplomatic intervention which will de-escalate the situation.
It's primarily aimed at making Boris Johnson look good, to the UK audience, and perhaps among NATO and other "western allies" (whether it will work is another question).
And if it distracts from some of his domestic worries, that's all to the good too, from his point of view.