As increasingly usual with supermarkets, they are overzealous when applying legislation.
Due to paracetamol OD'ing, a rule was brought in some considerable time ago whereby no more than 32 paracetamol tablets can be bought at a time. Tesco has applied this rule to include non-analgesics such as Sudafed (the one that does not include paracetamol). Obviously TheyKnowBest... it's like the 'produce ID if you're under 25 to buy alcohol' it's nannying, it's over zealous, it's TheyKnowBest and it's a PITA.
Morrisons now do it to include all analgesics.
Of course if you really want to OD on paracetamol there's nothing stopping you buying 2 packs from Tesco, popping along to Morrisons & buying 2 packs then pop along to Sainsbury, then to Waitrose, then to Boots, then to ANOther Pharmacy...
You're lucky the person let you make two separate purchases, I tore a strip off a jobsworthy oik in my local Tesco who insisted Sudafed was an analgesic & covered by the regulations. I have checked with a doctor, and they are not.
One more reason to not shop at Tesco.