1) Often, speakers do mention that their approach is either based on, or taken directly from, a particular commentary, but listeners generalize and assume that the quoted interpretation is the mainstream approach.
2) In speaking to young children, or even in many adult settings, it is reasonable to base an idea on one approach, even if it is not the only, or even the conventional one, to make a point. In many cases, to belabor the issue of whose opinion is which way, and whether or not it is generally accepted as ???? ???, is to obfuscate the main point of the speech and confuse the audience.
It is well known that there can be many different, even conflicting, interpretations of the same ???? ??”? or ????, all of which can be ???? ????? ????. The only caveat is that where the ???? has been decided in accordance with one opinion, we are bound to that side.
It should also be understood that when attending a shiur in Halacha, one should realize that the opinion of the speaker is not necessarily universally accepted, and one should always discuss any questions with his or her personal Rav.