I'm not sure East York was ever a township.
This was all York County (present day City of Toronto, Region of York. And the County was divided into either townships and the City of Toronto. Etobiocoke was Etobicoke Township. Scarborough was Scarborough Township. But as far as I know, York, East York, and North York were all just York Township. At least that was the case in the 1880s, and likely still in 1908 when Toronto East was annexed by Toronto.
Actually, East York *was* a Township--but only from 1924 onward, after the former York Township was split into three. (But it still doesn't disprove by "cities annex from townships, rather than vice versa" point--indeed, it was North York's creation two years earlier that led to East York itself incorporating, as successive Toronto annexations left the two remaining halves of York geographically unconnected.)
Oh, and York County wasn't just divided into townships and Toronto--there were other incorporated cities/towns/villages, from Toronto satellites like North/East/West Toronto, Weston, Leaside, etc, to Newmarket, Aurora, Richmond Hill, Markham, Woodbridge, Stouffville et al. And they all came about by being incorporated from/annexing from townships, often with a rhyme and reason that's casually lost to us today. (IOW, the Munro Park area south of the Grand Trunk yards would most likely have been an insular part of York Township before it was all annexed into Toronto. Bearing in mind that Victoria Park was *always* (East) York's eastern boundary, and had been from Simcoe times onward.)
Incidentally, a possible clue to why East York dips below Danforth at that point may be in the Ford plant that previously stood upon the Shopper's World site (cheap land + tax/regulation dodges?). And by the time Ford moved out, the municipal-annexation-by-dribs-and-drabs urge had passed--we were entering the Metro era, after all, where all was equal and boundaries were little more than fortuitous grandfathered-in lines on a map. The only remaining boundary changes of note were the amalgamating-away of the remaining towns and villages (whereupon Leaside became part of East York, and Forest Hill and Swansea joined Toronto); the addition of West Rouge to Scarborough in the 1970s; and mega-amalgamation in 1997...