PIP and Disability benefit from Lithuania

Morning all - struggling with EU co-ordination rules, does anyone have a view.

Client (not seen yet so some details a bit sketchy) is Lithuanian, came to UK in 2011, permanent right of residence granted 10/11/2016.
Has substantial mental health problems and has been in receipt of ESA and DLA for some years.  At the changeover to PIP info has been provided that he gets a disability benefit from Lithuania; has been in receipt since 1998 and Lithuanian authorities were aware of his move to the UK.  Not clear whether the client volunteered this info or DWP realised/found out.
Decision has been made that he does not qualify for PIP Daily Living because of the Lithuanian benefit and awarded 4 points for mobility.
He is still receiving ESA, in the Support Group but his benefit is being reduced by the value of the Lithuanian benefit.
Not sure I have the full gist of this but looks as though UK is not the competent state but does anyone think otherwise?
All thoughts gratefully received.

I had the same - disability benefit from Lithuania was used to reduce AA despite client being in receipt of AA for 7 years in the UK and had known of her disability benefit…ended with AA being withdrawn but thankfully no overpayment.