250w ballast with 400w bulb?

I found an add on craiglist for a 400w set up, guy wanted 200 I talked him down to 80. When I went to check out the ballast it had a 400w sticker that looked a bit out of place but the manufacturing sticker had the ballast stamped as 250w. Question. The ballast was powering a 400w bulb. Is that possible or did someone switch the ballast kit inside to 400w hence powering a 400w bulb.