Jayarava discusses this:
There is no doubt whatever that the find at Lumbini is significant and fascinating. But Coningham et al (and Coningham himself) have overstated the claims for what this find signifies. In particular it tells us nothing whatever about the dates of the Buddha. What it tells us about is the dates of human occupation and use of the site at Lumbini. This is intrinsically interesting, but is only an outline that requires considerable filling in. Specifically it tells us nothing about who the occupants were. The authors of the article seem to have been carried away by the minutiae of the discovery and the assumption that all archaeology on an Asokan site is ipso facto Buddhist.
We have no indication that the underlying layers were in fact Buddhist.
As I recall, scholarly consensus for the Buddha’s teaching career is 445 BCE to 400 BCE, give or take a decade or so.