Not a BSO
It looks reasonably well made
headset looks a bit gash though
If it's not too heavy, then it's not a BSO, just a mystery early Taiwan made commodity MTB
It'd be hard to age cos it looks like it's might have been put together with parts
The chainset is late '80s very early '90s but the frame could be later
Made in Taiwan and various details mean that it ain't a Peugeot - At least not a full catalogue model, that seat stay/seat tube lug arrangement says not a mian stream Peugeot to me
But the Alpina was an 'Exclusive for Halfords' so maybe?
What make are those thumbies? They are a big clue