EU businesses did multiple attempts to bypass Russian embargo and to sell their food products on the Russian market. This way Europeans framed the Belarusian government. These massive provocations by EU businesses resulted in a passport control on Belarus-Russia border that the Russian government had to introduce.
This ungrounded claim is consistent with recurring pro-Kremlin disinformation about West's attempts to bring discord in Belarus-Russia relations.
In the last years Russia indeed restricted control at the border with Belarus. It established a security zone with random border controls along the border with Belarus and moved flights to Belarus from domestic to international terminals. Given that the signing of the Agreement on mutual recognition of visas between Belarus and Russia is delayed, the issue of transit through Belarus-Russian border for third country nationals remains unresolved.
However, the Russian side has never named the re-export of EU embargoed food through Belarus as a reason behind the restrictions on moving through Belarus-Russia border. Instead Russian MFA cited "increased risks linked to terrorist and migration issues."