It's a Fujitsu dome with slider board, but not the more typical Fujitsu dome with slider switch observed in for example the Type 5c.
Companies other than BTC did use 1.25 u escape keys, but not nearly as prevalently. As Blaise pointed out, Focus started doing this during their second generation of keyboards and kept on doing it until the end as far as I'm aware. They're easy to distinguish however as BTC used lasered keycaps and very recognisable fonts, whereas Focus used doubleshots with what I think is standard Helvetica (or some other standard font).