I thought "cael" was used for being, or is that only passive tense.
Sorry this phrase is a mistake in the course, there is no useful translation of 'yn bod' as a sentence fragment, it is used in a number of different ways and the meaning always depends on the context.
I thought it was wrong, i have the modern welsh dictionary by Gareth King, and Welsh rules by Heini Gruffudd, and the only use of being is,
Form of Cael + noun + prefixed pronoun + noun, or
Yn/wedi + noun + cael + prefixed pronoun + noun