I'm not familiar with the local geography but, with a quick scan of the internet, I'd guess the naming is just a local coincidence, and Polkemmet Junction didn't have a direct relationship to the Polkemmet Colliery near Whitburn which supplied Ravenscraig's coking coal by rail.
The opening of railway lines around West Lothian looks quite complicated and convoluted, and generally was concerned with extracting & transporting minerals from the area. A good place to start with the history is the
Polkemmet Junction page on the RailScot website.
Long before the railways, Polkemmet country house and estate (now Polkemmet Country Park) had been a feature of the area. It had been the home of local landholders, the Baillie family, since the early 1600s.
The RailScot website says the first railway through the site of Polkemmet Junction was opened in 1850 by the Edinburgh & Glasgow Railway. This line approached Bathgate from the Longridge direction (Bathgate Chemical Works), not from Airdrie.
Then the Monklands Railway's Torbanehill and Bathgate branch opened in 1855, connecting to various coal and ironstone mines just west of Bathgate. This joined and left the existing E&G line at Polkemmet Junction, creating a 4-way junction. Presumably the Torbanehill mines were owed by the Baillie family, so maybe this is how the junction got its name. This 1856 map (available at the National Library of Scotland website) shows the various Torbanehill mineral lines in the area.
https://maps.nls.uk/view/74427801
The mineral line from the Torbanehill area was extended west in stages, reaching Airdrie in 1860 and subsequently was doubled in 1904.
The large colliery on Polkemmet Moor was only sunk at the time of the First World War and went into production in the 1920s, so long after Polkemmet Junction at Bathgate had opened.