The HV is correct.
When a child is not able to move around and explore their environment, it can have an affect on their language development. It just means that they have fewer experiences because they have to wait for new toys and activities to be brought to them, rather than seeing something and being able to go over and 'check it out'.
Think of a child crawling aound the room and all the different words they would hear from you in response to what they are doing. e.g. 'no, not the curtains', 'give the fork to mummy', 'what's in your mouth?', 'have you got daddy's phone?', etc
Try giving your ds choices of things to eat/wear/drink/play with. e.g. 'do you want banana or rice cake?'. When he indicates what he wants (through pointing or attempting the word) respond by saying the item he has chosen 'ds wants banana'.
Look at books. Talk about what is hapening in the pictures. Always use short, simple sentences - ''the dog is jumping'', ''the girl is in the mud''.
Talk about what he showing interest in. So the words he is hearing are linked to what he is thinking about. Walking down the road, ds points to a bus. 'Yes, it's a bus. Bye bye bus'.
Play 'ready, steady... go' games. Rolling a ball to him. Start to leave a gap before you say 'go' to give him a chance to try the word and then roll the ball. If he tries to say the word, roll the ball.
Work on 'more'. A very powerful word that can be used in a variety of situations. Tickle him, then stop. Ask 'more tickling?', when he responds in any way, tickle again. Repeat.
Do this with snacks, on a swing and anything that he enjoys.
Have a tea party with two toys - teddy and rabbit. Have tea plates, spoons, cups. You can use two word phrases 'teddy's drink', 'rabbits biscuit', Is this drink for teddy or rabbit?' 'oh, it's teddy's drink', etc
Look into a local nursery/playgroup as these can really help with developping language. Also, do you have any 'Talking Tots' groups near you. Have seen the material used and is very good.
Hope that helps a little.