Historical stream bed on this map is different. Its location and shape only very approximately resemble that of this current underground structure, doesn't it? In kitsendused.maaamet.ee it shows several parallel parts of water supply network, e.g. also a more direct one under Paju tänav. It's also unclear to me if the named stream really starts with way/673556403.

Jaamamõisa oja in this extent feels a little to speculative to me based on these data sources.
See also https://wiki.openstreetmap.org/wiki/Tag:location=underground#Concerns_with_verifiability