The novelisation of the film explicitly states that it is indeed intended to be a "thumbs-up" from BB-8
“Doing the best I can down here.” Rey vanished again. As soon as she
was out of sight, the grateful Finn gave BB-8 a thumbs-up. The droid
responded by shooting out a welding torch in imitation of the human’s
As does the 2017 Star Wars Annual
"After BB-8 reveals the location of the Resistance base, both exchange
As does the Star Wars: Absolutely Everything You Need to Know, Updated and Expanded edition
"Using his welding torch to give a thumbs up"
The original screenplay is slightly more ambiguous, but the intention seems pretty clear
Finn: Yeah, the Ileenium system, that's the one -- get us there as fast as you
A smiling Finn gives BB-8 a THUMBS UP. BB-8 quickly extends his
WELDING TORCH and TURNS IT UPWARD, then retracts it.
The film's special effects master, Neal Scanlan, explicitly confirmed in an interview with MTV.com that it was intended to be a 'thumbs up'.
"I think the reaction that BB-8 has to Finn would have been a
practical effect that we shot on the Milennium Falcon, but the
reaction to the thumbs up is something that definitely came later in
the day," Scanlan said.
"That thumbs up moment is exactly that," confirmed Guyett. "I think
it’s a real BB-8 and then we inserted a CG panel and its arm that came
out. So all of his tools, if you like, when he fires his wires and he
does that stuff, that’s sort of digital CG."
‘STAR WARS’: BB-8’S THUMBS UP MOMENT ALMOST DIDN’T HAPPEN