Or is this photo from a modern re-enactment of some sort? The archive this is from is supposed to be photos from that war. Are there other things in this photo (button? carabiner?) that mark it as more recent?
The source of that photo is the photo archive of the Finnish Defense Forces. The location is unknown ("tuntematon"), but they give the date as March 8, 1940.
There is a second photo which includes a satchel charge, explosives wrapped around a stick grenade.
...the breakaway metal ring is still on the neck of the bottle
Many Molotov Cocktails are improvised. That one was made at the bottling plant! And yes, the cap is aluminum.
Korkki oli alun perin alumiininen sinettikapseli ja myöhemmin bakeliittia, tiiviste korkkia tai vahattua pahvia.
Sotahistoriallinen aikakauskirja 24, p134
The cap was originally an aluminum seal capsule and later Bakelite, seal cap or waxed cardboard.
During the Winter War, Finland was so short of anti-tank weaponry that they began mass producing Molotov Cocktails. Various bottling plants, and eventually the state-owned alcohol monopoly stepped in to manufacture them.
In Sotahistoriallinen aikakauskirja 24, Keijo Heinonen writes in Who Invented The Molotov Cocktail?...
The bottle itself had been the half-litre vodka bottle used by Alko (the state alcohol monopoly) in 1934. A mixture of petrol and paraffin was chosen as the inflammable liquid, to which was added a small amount of tar. As a fuze, two ‘storm matches’, about 12 cm long, were attached to the sides of the bottle by two insulation tapes; the ties were further strengthened by wire.
The memoirs of Juho Niuk- kanen, minister of defence during the Winter War, give a lively description of how, having heard that it was technically possible, he directly ordered Alko to fill explosive bottles in its factories ‘until 40,000 bottles have been sent to the front’.
Alko took its task seriously. The initial contract for 40,000 had been de livered in the course of a few weeks. Deliveries continued throughout the Winter War so that by spring 1940 Alko had produced a total of 542,104 explosive bottles, some being ‘match’ bottles and others the so-called A bottles, in which an ignition ampoule was fitted inside the bottle.
Unlike the homemade "rag in a bottle of gasoline" versions, these were safer and more effective. You'd light the matches, throw the bottle, it would shatter on the target covering it in a sticky flammable mess which the lit matches would ignite.
An original Molotov Cocktail at the Rajamäki distillery