No I don't think the DL can begin without another present. I recall several years ago that I arrived for a service before anyone else - and it was already a couple of minutes past the scheduled hour to begin - the priest was relieved and dragged me to the chanter's stand, even though I had only recently been chrismated and had never before attended that particular service.
Something similar happened to me last year. I was living in an area where Oriental parishes were few and far between, and I had to figure out where to attend Liturgy on Holy Thursday. I decided on an Armenian parish: the parish schedule said it started at 10am, so I figured I could make it there with the long commute. When I arrived about fifteen minutes late, the priest was standing in the church alone. When he saw me, he ran up and gave me a big hug and said that, because the time is inconvenient for people's work schedules, no one showed up, and so he was worried he wouldn't be able to liturgize, and so he prayed that God would send him someone, and apparently God sent me. I told him he should have prayed harder, and he might've gotten an Armenian instead of a clueless Indian.
Anyway, we served the Liturgy together, just the two of us. Liturgically not as smooth as a normal Sunday Liturgy would've been with deacons and choir, but it was a sublime experience. Rarely have I seen a priest commune with such compunction.
He was new to the parish (less than half a year there, I think), so he just did the schedule the way he was told it was done last year. I suggested that he might try an early morning Liturgy next year that would end in time for people to go to work and see if that would work out better.
Re: the original post, I suspect that when the article says St Theophan served alone, it means he served with one person to assist him or at least be present. That "cell attendant" could be the one.