The "difference" is a stylistic and syntactic choice the speaker makes
There also is a fair amount of elision in spoken French. Any explanation that is going to fit in the space is going to be an over-generalization, but here goes. Stylistic choice is not rule-determined, of course, except for social rules of conversation that appreciate variety of expression (the spice of life). Syntactic choices, however, do obey certain rules. Specifically, and briefly: the verbe être is a copulative, rather than a "real" verb. That is, it joins what, in English, we call subjects and their predicates, and is used for descriptions (hence, the interrogative *comment*, which requests a description).
Whereas faire is the "dummy" action verb for French (that is, it stands in the place of an action verb, a "real" verb). Faire is also the way French most often separates the agent (who or what caused something to happen) from the entity that is actually "doing" the action. And because French favors being explicit about causatives, thus: je fais cuire les pommes de terre (where English would simply say: I am cooking the potatos), "faire" will show up a lot more often in French than in English.
Finally, to get back to interrogatives, *quoi* is the interrogative that stands for the object of a verb, that is, what is being affected by the action (in your example, the verb *ressembler à*). The answer, of course, would identify that something/someone: ça ressemble à mon grand-père de parler comme ça. (Note: the *de* introduces an infinitive action verb)
If you go back and look over your examples (they're really good ones, and you are being very observant to have picked up on them!), I think you will see how they connect with the être/faire distinctions, and with distinctions between description and identification.
[If this sounds pedantic, that's because I've been teaching this stuff fin colleges or an awfully long time...]
| Yolanda Broad|
Local time: 14:43
Native speaker of: English
PRO pts in pair: 1551