In that article, the BBC is clearly reporting (and states that it is reporting) Russian claims about the situation in Belgorod.
It does not say the reports are verified or corroborated in any way.
So it's not endorsing or supporting the claims, just stating what those claims are.
If there were a different account being offered by the Ukrainian government (for instance) the BBC would be reporting that but so far, the only statement the Ukrainian government have made about the matter, is to deny having anything to do with the incursion - a fact which the BBC is reporting on (see below).
Belgorod: Russian paramilitary group vows more incursions
By simply presenting the maskirova/propoganda (from either side) the BBC is not reporting news but acting as a vessel for state propoganda. There's no questioning, interrogation of facts, speaking with military analysts (plenty in the UK) or even exploring the video material that is available. Anyone skimming the headlines would get an entirely false picture. It has been heading this way for a long time. It's not just with regard to this conflict.