If you eliminate English "and" then "waiting" becomes a gerund in a construction Past Progressive Tense+Gerund. It just happens that English present participles and gerunds have the same ending. In Russian a gerund would be translated here as деепричастие/transgressive "ожидая": "мальчик стоял ожидая" (it sounds a little awkward though).
To compare, without that English feature: стоял=stood, ждал=waited. You can't say "The boy stood waited".
I think you understood incorrectly... There IS a Russian equivalent of Progressive Tense+Gerund (was standing waiting) which allows to eliminate AND, but while English present particle and gerund happen to have the same ending "-ing" so no ending is changed when you eliminate AND changing the second present particle into a gerund, the Russian equivalents (verb in past+transgressive) have different endings so you have to change an ending of the word becoming a transgressive.