Hi Clive,
Find attached an image of the illadopsis in question. You are not alone in thinking that Mountain doesn't occur at this site and I tend to agree with your supposition that these birds might be recent immigrants from other areas, which is understandable given the loss of forest habitat in the region over the past 30 years.
One minor corretion to Titus' records is that Yellow-whiskered Greenbuls were caught rather than Yellow-throated. Rather modestly, he also omitted my lifer that he pulled from the net - Grey-chested Babbler (definitely not an Illadopsis!).