Wist not (ouk ēidei). Past perfect of oida used as imperfect, did not know.
Followed (ēkolouthei). Imperfect active, kept on following as the angel had directed (Act 12:8). That it was true (hoti alēthes estin). Indirect assertion and so present tense retained. Note “true” (alēthes) in the sense of reality or actuality.
Which was done (to ginomenon). Present middle participle, that which was happening.
Thought he saw a vision (edokei horama blepein). Imperfect active, kept on thinking, puzzled as he was. Blepein is the infinitive in indirect assertion without the pronoun (he) expressed which could be either nominative in apposition with the subject as in Rom 1:22 or accusative of general reference as in Act 5:36; Act 8:9 (Robertson, Grammar, pp. 1036-40). Peter had had a vision in Joppa (Act 10:10) which Luke describes as an “ecstasy,” but here is objective fact, at least Luke thought so and makes that distinction. Peter will soon know whether he is still in the cell or not as we find out that a dream is only a dream when we wake up.