Learn Hardcore Japanese: sohu ha, sasimi yori tenpura no hou ga tabeyasui to yoku iimasu. - My grandfather often says tempura is easier to eat than sashimi.

The sentence is mainly about what your grandfather tends to say, not about identifying who the speaker is. If you used が, it could sound more like you are emphasizing that he is the one who says it.

So here, 祖父は is the natural topic-setting phrase.

Does 祖父 mean my grandfather here?

Yes, in a sentence like this, 祖父 usually means my grandfather.

In Japanese, when talking about your own family to other people, you often use plain family terms like:

祖父 = my grandfather
祖母 = my grandmother
父 = my father
母 = my mother

Using おじいさん for your own grandfather would usually sound less natural in this kind of context, because おじいさん is more respectful/polite and is often used for someone else’s grandfather, or for grandfather-like elderly men in general.

What does より do in this sentence?