Surely he did the right thing by stopping?
There is a potential for a collision as DA42 does not know the intent/clearence for the other a/c.
Without that info and being unable to query due to a busy frequency he must take the "safe" option until sure it's safe to proceed.
He has a doubt as to the safety in continuing.
I'm used to hearing the clearence for the taxying a/c including a phrase such as "the vacating traffic will give way to you".