Well, our system thinks you had other builds in your team running already - that’s the intended behavior if you are “full” on your allocated build concurrency (which is 1 team-wide for Starter teams, 3 for pro, and varies for Enterprise).
You can see if other builds are running on your build insights page, which you can find here: Netlify App
If you see it again, check that page to see if there are in fact other builds active. As far as I can tell, the last one that had that log (Netlify App) was actually seeing a different build in progress already from that page (Netlify App), so I think that was working as expected.