No I would say, you're not expected to play twice as fast just because you change the time signature of a melody from 4/4 to 2/4. It's supposed to have the same speed in bpm (e.g 100) regardless of if it's played in 5/4 or 7/12 beats per bar or whatever.
So you could just as well skip the line
in MidiFile::convertTimestampTicksToSeconds(). It won't change the tempo of the midi file, just eat cpu cycles. And after all, if the time signature event indeed was supposed to contribute to the timestamp calculations, wouldn't you have to inspect its content?