usage of "pfeifend" in the expression "der Mann wieder glücklich pfeifend den Weg entlang ging"

Question

I'm self studying German these days and learning grammar too.
In the sentence below, what's the grammatical form of pfeifend?
Is it something like present/past participle usage in English?
(like whistling as in Whistling his favorite song, He went along the street)

    Sie lachten beide zusammen und beobachteten, wie der Mann wieder glücklich pfeifend den Weg entlang ging.
==>  
    They both laughed together and watched the man whistling happily back down the path.

Answer 1

Pfeifend is the participle of pfeifen, that's true.

The participle describes the action of somebody while not addressing him directly like you would do in English.

And here's another style thing with your sentence: Although it's not incorrect to write Sie lachten beide zusammen, I wouldn't recommend it. Sie lachten zusammen or Sie lachten beide works just fine. To a native German-speaker, it sounds awkward if you use beide and zusammen in the same context.

Answer 2

You were close. "Pfeifend" is "Partizip Präsens" (present participle) of "pfeifen". In general, you obtain the "Partizip Präsens" by adding a "d" to the infinitive. As in English, you can use it like an adjective or an adverb. Note that you cannot use the "Partizip Präsens" like a "gerund" in German. In your example, "Pfeifend" is used as an adverb. Your translation misses a translation of the word "ging". I see no way to keep the "adverb" character of the participle and would say:

"... whistling happily and going back down the path. "