In Remarque's "Im Westen nichts Neues" ("All Quiet on the Western Front" in Wheen's translation)

I encountered this clause:

Der erste scheint wirklich verrückt geworden zu sein.

Which translated with deepl means:

The first one really seems to have gone mad.

But I have seen "verrückt geworden" before, although the auxiliary was "sein" and not "scheinen". So I was wondering why scheinen was being used as a auxiliary here or if I was missing something?