US Central Command is increasing the presence of mercenaries in Syria to make up for the withdrawal of regular troops. Only in the second half of June another 540 private military contractors arrived to the country, including commanders and instructors. The mercenaries are transported by car in groups of 12 to 16 people, and their task is mainly to form combat units loyal to Washington and protect oil and gas infrastructures.
The deployment of US private military contractors (PMC) in this war theatre is no secret: in 2018, the Pentagon acknowledged the presence of over 5,500 PMCs in Syria and Iraq. Therefore, claiming that "Russia found them" now is a deliberate distortion of facts. No evidence is provided to support the affirmation than their number is increasing or that 540 were sent to Syria last June.
Moreover, this so-called revelation coincides with reports about the presence of Russian ground troops fighting in Idlib, denied by Moscow. Mentioning PMCs' task of protecting hydrocarbon facilities is significant, since this is exactly what Russian private military contractors have been doing in Syria, and serves to fuel the recurrent Russian narrative of a US aggression to take over the resources of the country.
You can see other examples of disinformation about the US presence in Syria, such as its alleged plans to divide the country, its alleged support to jihadist groups, its alleged plundering of archaeological sites, its alleged role in fake chemical attacks or its alleged deliberate targeting of civilians.