Is your husband an employee or an independent contractor? If he's an employee, he should receive a W-2 for his annual wages and withholding. If he's an independent contractor, he would receive 1099 forms.
I'm guessing from what you wrote that he is an employee. What kind of work does he do? Would he have incurred $25K in expenses while doing his job? In some lines of work, that is legitimate. For example, my husband is an insurance damage appraiser. In 2011 and 2012, he was an employee of a company, but he worked out of our home and spent all day on the road driving to see wrecked cars. He was able to claim all of his work mileage, plus a home office deduction and other deductions for work expenses (his phone, computer etc.) as unreimbursed work expenses, just like he would have claimed them as business expenses if he were an independent contractor on a 1099.
So knowing what your husband does for work and what those unreimbursed expenses are (there is a schedule that lists them) is important.
The $5000 isn't "extra dollars," that's what he was claiming was his taxable income for the year. He would have been responsible for paying income taxes on that amount (approximately - there are other deductions, etc. that can come into play). If what was witheld from his paychecks equalled more than the tax due on his adjusted gross income, then he was entitled to a refund. Without knowing how much was witheld, it's impossible to know whether or not that $1700 was correct.
The tax forms will list what the refund is and where it went. The IRS can't issue a refund without that information.
Basically...there's no way to tell from the info you gave whether or not anything shady is going on or if you just don't understand what you're looking at.
ETA: There is a schedule called 2106 that will list out the unreimbursed employee expenses. If business use of the home was part of this, there is a worksheet called Employee Home Office Worksheet that is used to calculate this.