Doesn’t say “exclusively from others”. Without casting this spell you couldn’t do that normally.

It also doesn't say that you cannot fly yet that doesn't mean it gives you a flying speed. The spell only does what it says it does: It makes you able to siphon life force from others. In any situation not explicitly mentioned in the spell you are still bound by all of the other game rules and as far as I know there is no rule that'd say you can go siphoning life forces from anything without an effect explicitly stating that you can do so.

The D&D rules do not run on a principle of "you can do absolutely anything except for what is explicitly forbidden".

No qualifiers about the target having to be a creature other than you. It just has to be a creature within your reach.

You do not get to cherrypick which sentences of the spell description you read and follow. It does quite explicitly state "can siphon life force from others to heal your wounds". There is no concept of flavor text in 5e, every word of a spell description is rules.