'continue' as used by tower controler

I was returning to my home base this morning and was cleared down to 4500'
from 5500' by Tucson approach (pattern altitude is 3400'). On the handoff
to the tower I called in and said I was 'through 5300'. The only words back
from the Tower were 'Cherokee 54405, continue'. This was the first time I
had received this instruction and assumed (yes, bad idea) that I was being
told to continue inbound to the pattern. I leveled at 4500' and continued
inbound. As I got closer to the pattern I asked the tower controller if I
could descend to pattern altitude. He replied that he had given me
permission on first contact. I continued on down and landed.

Is this a commonly used phraseology from ATC? I would have thought just
using the word 'continue' would be too ambiguous for the likes of the FAA.

--
Regards,
Mike

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