Are My Electrical Boxes Actually Grounded?
Well it is possible this home is a expanded metal stucco home and just happens to have some pipe touching the metal looking like a ground, it can also be possible that the boxes are grounded from the back side, your location in the world would be helpful but with cloth covered wiring I would suggest you add a grounding electrode other than your water pipe (the most common method for the decade prior and after your home was built) it has been legal to add a ground separately to these circuits.
I would not trust the chance there is a ground but adding a GFCI at the breaker or first outlet on the string or chain you can then install 3 pronged receptacles and just put the sticker that comes with the GFCI on the new 3 prong that’s states GFCI protected no equipment ground. Yes the stickers fall off but this is a legal way to update a 2 wire system, if you add a ground that is the best way but also the most expensive and usually only done when remodeling/ redecorating (big difference between the 2 names and code requirements BTW.