Yes yes yes. Bultaco's were some of the most successful vintage race bikes , particularly in the MX and trials and enduro events. Their road bikes were awesome, though. That thing is definitely not worth $5k, and doesn't look like much of a race bike...perhaps amateur racing, but that seat, the headlight, the kickstand and the lack of safety wiring say it was never a real AHRMA racer.
Sweet, sweet bike, though, I would love to have one (I really want a TSS). If it's a decent deal I totally go for it, I don't think you'll be disappointed. Make sure it's in good mechanical shapre; the amateur racing bit would make me somewhat cautious, but it might be in fine shape.