Forum:Inferno reckless sommon ?

Please clearify me about this. I read the explaination of the card carefully. The card is "Inferno Reckless Summon" I really suspect about it gramatical.

[You can only activate this card when 1 monster with an ATK of 1500 points or less is Special Summoned to your side of the field while there is a face-up monster on your opponent's side of the field. Special Summon all cards with the same name as the Summoned monster from your hand, Deck, and Graveyard in face-up Attack Position. Your opponent selects 1 monster on their side of the field and Special Summons all cards with that same name from their hand, Deck, and Graveyard.]

What I want to ask is about this sentence

"While there is a face-up monster on your opponent's side of the field."

Is this mean the opponent must have only 1 monster on his field? So, why in the other sentence is imply that

"Your opponent selects 1 monster on their side of the field"

Why the opponent have to choose if there is only single monster on the field? In my view, I think that there may have some wrong translation from japanese into English. Because in the Japanese there is no Plural and singular verb. So, does the card explaination mean that the opponent must have at least 1 monster on his side of the field and forgot to put the word "at least 1" on this explaination. Please help me,Thank you anyway